The purpose of this work is to understand the molecular events regulating the differentiation of embryonic chick lens cells and the role of the lens transparency. Within this fiscal year, we have shown 1) that the regulation of gamma-crystallin gene expression can be uncoupled from lens cell elongation, 2) that the specialization of gamma-crystallin synthesis in differentiating chick lens cells is not solely a function of the amount of gamma-crystallin mRNA present in the cells, 3) that embryonic chick gamma-crystallin contains at least two distinct polypeptides which have similar tryptic peptides, 4) that the ratio of synthesis of these two gamma-crystallin polypeptides is reversibly and markedly changed during the initiation of lens cataract formation in culture, and 5) that cortical cataract formation and the associated changes in gamma-crystallin synthesis can be prevented in cultured lenses by maintaining the normal vitreous-lens relationship. BIBLIOGRAPHIC REFERENCES: Beebe, D.C. and Piatigorsky, J.: Differential Synthesis of Crystallin and Noncrystallin Polypeptides During Lens Fiber Cell Differentiation in vitro. Exp. Eye Res. 22: 237-249, 1976. Milstone, L.M. and Piatigorsky, J.: Delta-Crystallin Gene Expression in Embryonic Chick Lens Epithelia Cultured in the Presence of Insulin. Exp. Cell Res. 105: 9-14, 1977.